I have reviewed this draft.
I think it is in good shape and can move forward once we resolve one
issue. Here's the issue:
A node that forwards a flow whose flow label value in arriving
packets is zero MAY change the flow label value. In that case, it is
RECOMMENDED that the forwarding node sets the flow label field for a
flow to a uniformly distributed value as just described for source
nodes.
o The same considerations apply as to source hosts setting the flow
label; in particular, the normal case is that a flow is defined by
the 5-tuple.
o This option, if implemented, would presumably be used by first-hop
or ingress routers. It might place a considerable per-packet
processing load on them, even if they adopted a stateless method
of flow identification and label assignment. This is why the
principal recommendation is that the source host should set the
label.
I think this recommendation is problematic. I agree that the first hop
router should insert the flow label, but requiring it to do fragment
reassembly in order to find the 5-tuple is a big burden, and I'm not
sure its even called for.
The RFC 2119 language above is fine. But I'd like to change the part
about normal case being the 5-tuple. I think the normal case should be
the 2-tuple under these circumstances. The source has access to the
5-tuple; a router is not guaranteed to have access to it.
In addition, I'm not sure I understand how a router knows that it is a
first hop router. Are there cases where a device might mistakenly
believe it is a first hop router at a point where the traffic has
already been load-balanced to multiple routers? Are there situations
where the multiple first hop routers are used from the same host? The
document should provide some guidance about operational conditions where
the recommendations for the first hop router can be applied. The
document should state how such functionality is turned on (per
configuration? automatically?) and provide assurances that problematic
conditions can be avoided.
Jari
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